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Abstract

Suspended-core fibers are systematically studied. We show that confinement loss in suspended-core fibers can be effectively reduced by an increase of air-cladding width for even sub-micron core diameters and, therefore, provides a considerable simpler solution than equivalent photonic crystal fibers with a large number of air holes for a wide range of nonlinear applications. We have further demonstrated a suspended-core silica fiber with core diameters of 1.27µm and sub-dB splice loss to Hi1060. Loss at 1.55µm was measured in this fiber to be 0.078dB/m, a record for this small core diameter, limited mainly by scattering loss at the glass and air interface. The combination of high nonlinearity, low splice loss and low transmission loss of the suspended core silica fibers will enable a new class of low loss all-fiber nonlinear devices.

(a). Waveguide dispersion in step-index fibers with various NAs, (b) Material dispersion of fused silica, along with the minimum 1st zero dispersion wavelengths λ01 marked out by symbols for step-index fibers with various NAs. The V value of each fiber required to achieve the minimum λ01 is listed in the legends.

Confinement loss of SCFs with air-cladding width d=5, 7.5, 10, 12.5, and 15µm, lines with symbols, are shown on right vertical axis. Corresponding waveguide dispersions, lines, are shown on left vertical axis. The dispersion curves remain mostly the same with a change of d.

(a). Confinement loss versus normalized air-cladding width d/2ρ at various normalized wavelengths, λ/2ρ. Simulation is performed for 2ρ=1µm at various wavelengths. (b). Normalized field for d=15µm and 2ρ=1µm at various normalized wavelengths.

Measured loss for three fibers; SCF1: 2ρ=2.3µm, no germanium in the core; SCF2: 2ρ=2.3µm, germanium doped center of ~60% core radius, graded refractive index with NA=0.275, SCF3: 2ρ=1.27µm, with germanium-doped center similar to SCF2. Close up of SCF1 is essentially the same as SCF2. A global view is used to show the whole fiber instead. The solid line fit is of the formula: A+B/λ3.

Measured dispersion and simulated Multipole result with using six air holes as shown in the bottom inset. Index difference between the two polarization modes is also shown. A simulated mode at 1.05µm is also shown in the bottom inset. The top inset shows measured fringe pattern from interference of the two birefringence modes.